1. Field of the Invention
The present invention relates to a thin film magnetic head, a head gimbal assembly, a head arm assembly and a magnetic disk drive comprising a magnetoresistive device which includes a fixing layer made of an iridium-manganese alloy (IrMn), and a method of driving such a magnetoresistive device.
2. Description of the Related Art
Conventionally, magnetic disk drives are used as devices recording and reading magnetic information (hereinafter simply referred to as information). The magnetic disk drive comprises, for example, a magnetic disk in which information is stored and a thin film magnetic head which records information onto the magnetic disk and reproduces information recorded on the magnetic disk in an enclosure. The thin film magnetic head comprises a recording head including an air bearing surface (ABS) which faces the magnetic disk and a reproducing head. The reproducing head includes a giant magnetoresistive device (GMR device) exhibiting a giant magnetoresistive (GMR) effect. In particular, a spin-valve (SV) type GMR device is generally used.
The SV type GMR device (SV-GMR device) comprises a SV film with a structure in which a magnetic layer (magnetization fixed layer) of which the magnetization direction is fixed in a predetermined direction and a magnetic layer (magnetization free layer) of which the magnetization direction changes depending upon a signal magnetic field from the magnetic disk are laminated with a non-magnetic intermediate layer in between, and in the SV-GMR device, at the time of reproducing, a sense current flows into an in-plane direction of a laminate. Such a GMR device is specifically called a CIP (Current in Plane)-GMR device. In this case, when a sense current flows depending upon a relative angle between the magnetization directions of two magnetic layers (the magnetization fixed layer and the magnetization free layer) in the SV film, electrical resistance (that is, voltage) changes. The magnetization fixed layer is disposed adjacent to a fixing layer made of an antiferromagnetic material. The fixing layer is exchange coupled to the magnetization fixed layer through producing an exchange coupling force between the fixing layer and the magnetization fixed layer. The characteristics or reliability of the SV-GMR device depends upon the magnitude of the exchange coupling force or thermostability, so in order to improve the exchange coupling force and heat resistance, an antiferromagnetic layer using a nickel-manganese alloy (NiMn) or a platinum-manganese alloy (PtMn) has been widely adopted.
Moreover, a SV-GMR device in which a magnetization fixed layer has a three-layer synthetic structure including two ferromagnetic layers (a first ferromagnetic layer and a second ferromagnetic layer) and a non-magnetic intermediate layer disposed between the ferromagnetic layers to produce a strong exchange coupling force between the first and the second ferromagnetic layers, thereby an exchange coupling force with the antiferromagnetic layer is effectively increased has been proposed (for example, refer to Japanese Unexamined Patent Application Publication No. 2000-137906). Further, a SV-GMR device in which a matching layer is inserted between an antiferromagnetic layer and a magnetization fixed layer to increase an exchange coupling force has been disclosed (for example, refer to Japanese Unexamined Patent Application Publication No. Hei 9-82524).
In recent years, a reduction in the profile of a thin film magnetic head (the width of a gap) has been strongly required according to an increase in the recording density (capacity) of a magnetic disk. However, in the case where an ordered alloy (a material requiring a regular atomic arrangement to develop an antiferromagnetic property) such as NiMn or PtMn which is described above is used for an antiferromagnetic layer, in order to secure a sufficient exchange coupling force, the antiferromagnetic layer made of the ordered alloy is required to have a thickness of approximately 10 nm, so the thin film magnetic head cannot sufficiently respond to a demand for a reduction in the profile. Moreover, the thickness of the antiferromagnetic layer forms a relatively high proportion of the total thickness of the SV-GMR device, so when the thicknesses of layers except for the antiferromagnetic layer are reduced to reduce the total thickness of the SV-GMR device, the ratio of a sense current flowing through the antiferromagnetic layer is relatively large, thereby it results in a decline in output as a reproducing head.
On the other hand, a SV-GMR device in which an iridium-manganese alloy (IrMn) is used for an antiferromagnetic layer has been disclosed (for example, refer to Japanese Unexamined Patent Application Publication No. Hei 9-148132). The antiferromagnetic layer using IrMn can obtain a sufficient exchange coupling force with a magnetization fixed layer, even if the antiferromagnetic layer has a thickness of less than 10 nm, and as a result, a decline in output as a reproducing head can be prevented.
However, even in the SV-GMR device in Japanese Unexamined Patent Application Publication No. Hei 9-148132, when the antiferromagnetic layer has a thickness of less than 10 nm, its heat resistance is not sufficient. For example, in a high temperature environment of 200° C. or more, an exchange coupling force between the antiferromagnetic layer and the magnetization fixed layer may be reduced.